A representative enzyme oxidizing saccharide is a glucose oxidase which oxidizes glucose, and such a glucose oxidase is widely used in various fields.
For example in a dry egg white manufacturing process, a glucose oxidase is used for the purpose of removing the glucose in the egg white (desugaring). Since the dry egg white can be stored for a longer period when compared with a raw egg white and enables a lower cost for transportation and a smaller space for storage, it is used as a starting material for various food products. The glucose contained in such a dry egg white undergoes a reaction with an amino group in the egg protein during the storage to allow a Maillard reaction to occur, resulting in a brown color and an unpleasant odor. In order to avoid such a deterioration of the quality, a fermentation method using glucose oxidases or yeast for the purpose of removing of the glucose in the egg white is used.
On the other hand, the glucose oxidase has a relatively high thermostability, which allows the glucose oxidase activity to remain in a product. For example, when the glucose oxidase activity remains in the dry egg white, it results in a problematic oxidization of the glucose in a starting material during the manufacture of confectioneries using the dry egg white. On the contrary, a heat treatment under a condition allowing the glucose oxidase to be inactivated results in coagulation of the egg white, which leads to a problematic deterioration of the commercial value of the dry egg white. The desugaring by fermentation of the yeast also results in a problem due to a fermentation odor remaining in the dry egg white product.
Also in a bakery or flour milling plant, for enhancing the sintering performance of a flour or for making a kneaded flour having desirable strength and stability by improving the elasticity, a glucose oxidase is used. This effect is believed to be supported by a mechanism in which the glucose in the flour mixture is oxidized to produce gluconolacton and hydrogen peroxide and the hydrogen peroxide thus produced acts as an oxidizer thereby contributing to the formation of a gluten S—S bond. As a result, the protein acquires a further stable form, thereby improving the quality of the kneaded flour, the capacity of the sintered product, and the core structure.
For example, Patent Document 1 typically discloses a technology which involves addition of a glucose oxidase to a cereal flour to improve the rheological characteristics of the kneaded flour, texture and appearance of the sintered bread. Also in Patent Document 2, a preparation for improving the quality of a bread containing a cellulase and a glucose oxidase is disclosed. In addition, Patent Document 3 discloses a bread improver containing a glucose oxidase and a lipase and a baking method using the same.
While the glucose oxidase is used in various applications as described above, it is problematically less effective on a material containing no or small amount of glucose because it is an enzyme which oxidizes the glucose exclusively. In addition, no effect can be achieved when another saccharide such as lactose is contained unless an enzyme capable of decomposing such another saccharide into the glucose, such as a lactase, is used in combination.
For example, use of a glucose oxidase as an additive for improving a kneaded flour and a bread requires the presence of glucose as a substrate, whose content in a wheat flour is as low as 0 to 0.4% by weight, which poses a limitation of the usefulness of the glucose oxidase. On the other hand, a maltose content of the flour of a cereal plant is known to be higher than the glucose content.
For the purpose of solving the aforementioned problems, much attention has been focused on a saccharide oxidase effective on saccharides other than the glucose. For example, Patent Document 4 discloses a technology relating to an oligosaccharide oxidase exhibiting a satisfactory reaction activity on respective substrates of D-glucose, D-lactose, D-cellobiose, D-maltotriose, D-maltotetraose, D-maltopentaose, D-maltohexaose, and D-maltoheptaose. In addition, Patent Document 5 discloses a technology for improving the characteristics of a dough or a bread by using a saccharide oxidase derived from a microorganism belonging to genus Microdochium which oxidizes a maltodextrin or a cellodextrin preferentially over the glucose.